Providing power continuously from a renewable primary energy source requires energy storage. Ideally, the storage should supply the same power level as the primary source, as well as be available on demand in a dispatchable manner. Many energy storage technologies are known in the industry such as battery, rotating-machinery, pumped-hydro, compressed air, hydrogen production and storage fluids, such as molten salt.
The molten-salt storage system designs usually have a double storage tank layout, a “hot tank” for salt recently heated and a “cold tank” for salt awaiting heating. The temperatures of the two tanks typically differ by 100° C. or more for acceptable stored energy density and heat exchanger efficiency. It is known in the art, for example, that thermal heat storage systems employing transport fluids at high temperatures can achieve hot-tank temperatures up to 500-600° C. or more. Accomplishing this using a transfer fluid, however, entails the use of pipes, pumps, etc., that can increase operational complexity. The molten-salt storage fluid is, itself, commonly used as the transfer fluid pumped between the primary power source, the storage tanks and the heat exchanger for electrical generation equipment. As well as the operational complexity, there is a risk of the salt freezing in the transfer pipes connecting the various components that imply heat wrapping, nighttime draining, or the like.
Solar and wind energy are included among renewable energy sources. Solar energy plants using solar radiation concentrating systems in conjunction with thermal heat storage devices is known in the art. The use of other liquid transfer fluids such as water, fluoride salt and other metal containing materials in thermal heat storage devices is also known in the art.